Neil Lennon has admitted he cannot afford another defeat if he is to stay in contention to become Celtic's ­manager permanently. Photograph: Craig Halkett/PA

Neil Lennon admits he cannot afford another defeat if he is to stay in contention to become Celtic's manager permanently.

Celtic's embarrassing Scottish Cup semi-final defeat by Ross Countytriggered the widespread theory that Lennon, the interim manager, had virtually no chance of being given the post full-time. Yet the former club captain has guided Celtic to four successive Premier League victories for the first time in more than a year and has key allies within the boardroom.

As those directors say that no other candidate will be approached until the end of the season, Lennon's SPL form is pertinent but the man himself is fully aware of potential disappointment.

"I'm just one game away from being in a pretty precarious position again," Lennon said. "I've seen improvement but you're always worried there's a Ross County performance around the corner.

"Am I one defeat away from people thinking I shouldn't get the job? Probably. It's like a swing-o-meter in the election."

Lennon challenged his players to show him they should not be part of a summer clear-out after that County defeat. Victory at Dundee United on Sunday would at least secure second place in the league and a Champions League qualifying place.

"We've won four in a row but, if we lose on Sunday, we're back to square oneagain," said the Irishman. "That's just the nature of the position I'm in. I don't want to dwell on Ross County too much, as it's done, but I've asked them to prove me wrong. They're starting to do that now. But that's a minimum prerequisite: do your talent justice, which I felt they've not done on a number of occasions this season."

The deeper meaning to tomorrow relates to the destination of the SPL trophy. Rangers will finally be crowned champions if Celtic fail to win in Dundee or Rangers win at Hibernian later in the afternoon.

"I want to prolong Rangers' wait for the title as long as I can," added Lennon. "I want to make them go to Easter Road to get whatever they need. So we have to win the game. Plus we have our own agenda of wanting to get second place and keep Dundee United away from us. We want to make Rangers sweat that wee bit longer."